Rotorcraft rotor blade assembly

ABSTRACT

A rotorcraft rotor blade assembly includes an upper skin portion extending substantially a full span of the rotor blade assembly and a lower skin portion extending substantially the full span of the rotor blade assembly. Each of the upper skin portion and the lower skin portion is configured to carry at least substantially 30% of rotor blade assembly loads.

TECHNICAL FIELD

This specification relates to rotor blade assemblies, for example,assemblies of main rotor blades or other rotor blades, of a rotorcraft.

BACKGROUND

Rotorcrafts such as helicopters include rotor blades, for example, mainrotor blades and tail rotor blades. A conventional rotorcraft rotorblade derives a vast majority of its strength and stiffness from aninternal torque tube, often referred to as a spar or D-spar. Theremaining volume within a rotor blade is occupied, in part, by a coremade of a material such as honeycomb core. An upper skin portion and alower skin portion are adhesively bonded to the spar and core. In such aconventional rotor blade, skins are members whose curvature createsaerodynamic loads as the outer contour interacts with fluid. Such skinsare thin and serve as aerodynamic fairings that provide a proportionallysmall amount of the load carrying capability of the rotor blade.

SUMMARY

This specification describes technologies relating to rotorcraft rotorblade assemblies. Some examples of the rotorcraft rotor blade assembliesdescribed here can include a stub spar that spans less than a full spanof the rotor blade. Some examples of the rotorcraft rotor bladeassemblies described here can include thick skins Some examples of therotorcraft rotor blade assemblies described here can includecombinations of a stub spar and thick skins

Certain aspects of the subject matter described here can be implementedas a rotorcraft rotor blade assembly. The rotorcraft rotor bladeassembly includes an upper skin portion and a lower skin portion. Theupper skin portion extends substantially a full span of the rotor bladeassembly. The lower skin portion extends substantially a full span ofthe rotor blade assembly. Each of the upper skin portion and the lowerskin portion is configured to carry at least substantially 30% of rotorblade assembly loads.

This, and other aspects, can include one or more of the followingfeatures. Each of the upper skin portion and the lower skin portion isconfigured to carry at least substantially 30% of rotor blade assemblyloads by less than substantially 50% of the full span of the rotor bladeassembly. Each of the upper skin portion and the lower skin portiontapers from an inboard end of the rotor blade assembly towards theoutboard end. A thickness of each of the upper skin portion and thelower skin portion at an inboard end of the rotor blade assembly isabout ten times a thickness of each of the upper skin portion and thelower skin portion at an outboard end of the rotor blade assembly. Tocarry at least substantially 30% of rotor blade assembly loads, each ofthe upper skin portion and the lower skin portion includes compositematerial fibers oriented to carry torsional rotor blade assembly loadsand centrifugal rotor blade assembly loads. The rotor blade assemblyexcludes a spar. Alternatively, the rotor blade assembly includes a stubspar which extends less than a full span of the rotor blade assembly.The stub spar extends up to 50% of the full span of the rotor bladeassembly. The stub spar is positioned at an inboard end of the rotorblade assembly. The stub spar tapers as the stub spar extends away fromthe inboard end of the rotor blade assembly. A ratio of a quantity ofupper skin portion material and lower skin portion material to aquantity of stub spar material at the inboard end is about 60:40. Theratio increases along the full span of the rotor blade assembly from theinboard end to the outboard end.

Certain aspects of the subject matter described here can be implementedas a method of manufacturing a rotor blade assembly. An upper skinportion is formed to extend substantially a full span of the rotor bladeassembly. A lower skin portion is formed to extend substantially thefull span of the rotor blade assembly. Each of the upper skin portionand the lower skin portion includes composite material to carry at leastsubstantially 30% of rotor blade assembly loads. The upper skin portionis attached to the lower skin portion.

This, and other aspects, can include one or more of the followingfeatures. To form the upper skin portion and the lower skin portion,composite material to carry at least substantially 30% of rotor bladeassembly loads by less than substantially 50% of the full span of therotor blade assembly can be included in each of the upper skin portionand the lower skin portion. Each of the upper skin portion and the lowerskin portion can be formed to taper from an inboard end of the rotorblade assembly towards the outboard end. Each of the upper skin portionand the lower skin portion is formed such that a thickness of each ofthe upper skin portion and the lower skin portion at an inboard end ofthe rotor blade assembly is about ten times a thickness of each of theupper skin portion and the lower skin portion at an outboard end of therotor blade assembly. A stub spar is positioned between the upper skinportion and the lower skin portion. The stub spar extends less than afull span of the rotor blade assembly. The upper skin portion and thelower skin portion are attached to the stub spar. The stub spar extendsup to 50% of the full span of the rotor blade assembly. The stub spar isformed to taper as the stub spar extends away from the inboard end ofthe rotor blade assembly. A ratio of a quantity of upper skin portionmaterial and lower skin portion material to a quantity of stub sparmaterial at the inboard end is about 60:40. The ratio increases alongthe full span of the rotor blade assembly from the inboard end to theoutboard end.

The details of one or more implementations of the subject matterdescribed in this specification are set forth in the accompanyingdrawings and the description below. Other features, aspects, andadvantages of the subject matter will become apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1E are example plots showing loads on a rotor blade.

FIG. 2A is an example plot showing, for a conventional rotor blade, adistribution of different materials of the rotor blade.

FIG. 2B is an example plot showing a distribution of different materialsof a rotor blade having a stub spar with thick skins.

FIG. 2C is an example plot showing a distribution of different materialsof a rotor blade having a stub spar with thin skins.

FIG. 2D is an example plot showing a distribution of different materialsof a rotor blade having thick skins but no stub spar.

FIGS. 3A-3C show plots of material distribution along the span of suchan example rotor blade assembly.

FIG. 4 is a schematic drawing of an example rotor blade assembly.

FIGS. 5A-5C show cross-sections of the rotor blade assembly at differentlengths along the full span of the assembly.

FIGS. 6A-6C show cross-sections of examples of stub spars.

FIG. 7 is a flowchart of a process of manufacturing a rotor bladeassembly.

FIG. 8 is a schematic drawing of an example rotor blade assembly withouta stub spar.

FIG. 9 is a flowchart of a process of manufacturing a rotor bladeassembly.

DETAILED DESCRIPTION

A conventional rotorcraft rotor blade derives a vast majority of itsstrength and stiffness from an internal torque tube, often referred toas a spar or D-spar. The remaining volume within a rotor blade isoccupied, in part, by a core made of a material such as honeycomb core.An upper skin portion and a lower skin portion are adhesively bonded tothe spar and core. In such a conventional rotor blade, skins are memberswhose curvature create aerodynamic loads as the outer contour interactswith fluid. Such skins are thin and serve as aerodynamic fairings thatprovide little, if any, structural stiffness to the rotor blade.

A rotor blade can include different types of material, for example,centrifugal material, torque material, shear material or other material.Centrifugal material can include, for example, composite material (suchas fibers or other composite material) aligned substantially span-wiseon the span of the rotor blade and configured to carry centrifugal loadson the rotor blade. Torque material can include, for example, compositematerial (such as fibers or other composite material) torsionally wound(for example, around the spar or around the skin or both), along thespan of the blade. Shear material can include, for example, compositematerial (such as fibers or other composite material) which serves tocapture and direct energy from outboard discrete elements, for example,abrasion strip, trailing edge or other elements, toward the blade attachbolt hole locations near the inboard end where all blade loads resolve.The shear material can include a combination of dominantly torquematerial and some centrifugal material or chord-wise material (or both).

FIGS. 1A-1E are example plots showing loads on a rotor blade. Each ofFIG. 1A, FIG. 1B, FIG. 1C, FIG. 1D and FIG. 1E show centrifugal loads,chord loads, beam loads, torsion, and hard detail, respectively, along aspan of a rotor blade. FIG. 2A is an example plot showing, for aconventional rotor blade, a distribution of different materials of therotor blade. As shown in FIG. 2A, the spar, which spans substantially anentire span of the rotor blade, is configured to carry a significantportion of centrifugal, torsional and shearing loads. To do so, the sparis manufactured to include sufficient quantities of centrifugalmaterial, torsional material and shear material. In comparison, the skinmaterial is configured to carry significantly smaller quantities of theloads because the skins do not serve as significant structural elementsin the conventional rotor blade. Therefore, the skins are manufacturedto include significantly smaller quantities of material relative to thespar. Thus, the total load carried by the conventional rotor blade isdominantly carried by the spar compared to the skins.

This application describes alternative rotor blade assemblies in whichthe skins carry a significantly greater portion of the loads compared tothe conventional rotor blade. FIG. 2B is an example plot showing adistribution of different materials of one such rotor blade assembly,which has a stub spar with thick skins FIG. 2C is an example plotshowing a distribution of different materials of another such rotorblade assembly, which has a stub spar with thin skins FIG. 2D is anexample plot showing a distribution of different materials of anotherrotor blade assembly, which has thick skins but no stub spar. Details ofsuch rotor blade assemblies are described below.

FIGS. 3A-3C show plots of material distribution along the span of suchan alternative blade assembly. FIG. 3A shows a quantity of centrifugalmaterial in the skins. Compared to the quantity of centrifugal materialsin the skins of a conventional rotor blade (FIG. 2), the quantity ofcentrifugal materials in the skins of the alternative rotor bladeassembly is greater. In particular, the quantity of centrifugalmaterials is greater near an inboard end of the blade and decreasestowards the outboard end of the blade. FIG. 3B shows that a quantity oftorque material in the spar. Compared to the quantity of torque materialin the spar of a conventional rotor blade (FIG. 2), the quantity oftorque material in the spar of the alternative rotor blade assembly canbe the same or less. In addition, compared to the quantity of torquematerial in the skins of a conventional rotor blade (FIG. 2), thequantity of torque material in the skins of the alternative rotor bladeassembly is greater. Consequently, the quantity of the torque materialis substantially constant along the span of the rotor blade. Thequantity of shear material in the conventional rotor blade (FIG. 2) andthe alternative rotor blade assembly can be substantially the same. Inparticular, FIG. 3C shows that a quantity of shear material is greaternear the inboard end of the rotor blade and decreases towards theoutboard end of the rotor blade with a tapering down along the span.

Thus, this application describes a rotor blade assembly and methods ofmanufacturing the rotor blade assembly by which the total load carriedmostly by the spar of a conventional rotor blade is now split intoconstituent loads (for example, centrifugal loads, torsional loads,shearing loads), each of which is partially carried by the spar and theskins. As described below, the spar of the alternative rotor bladeassembly can, consequently, be thinner than and manufactured usinglesser material compared to the spar of the conventional rotor blade.Because complexity and cost of manufacture increases exponentially withthickness, the alternative rotor blade assembly can be easier andcheaper to manufacture compared to the conventional rotor blade. Forexample, a spar that has half the thickness of a spar of theconventional rotor blade assembly may cost one-quarter or one-sixteenththe cost of the spar of the conventional rotor blade. Disassembling andinspecting the alternative rotor blade assembly can also be simplifiedrelative to the conventional rotor blade.

I. Rotor Blade Assembly Including a Stub Spar

FIG. 4 is a schematic drawing of an example rotor blade assembly 100.The assembly 100 includes a stub spar 102 extending less than a fullspan of the assembly 100. The assembly 100 includes an upper skinportion 104 and a lower skin portion 106, each extending substantiallythe full span of the assembly 100. The stub spar 102 is positionedbetween the upper skin portion 104 and the lower skin portion 106. Insome implementations, the stub spar 102 can extend up to the near amiddle of the full span of the assembly 100. The full span of theassembly 100 can extend from an inboard end 108 of the assembly 100 toan outboard end 110 of the assembly 100.

Near the middle of the full span of the assembly 100 can be, forexample, 50% of the full span of the assembly 100 or substantially 50%of the full span of the assembly 100. Having the stub spar 102 spansubstantially 50% of the full span of the assembly 100 can includehaving the stub spar 102 extend between 10% and less than 50% (forexample, substantially one-tenth to one-third) of the full span of theassembly 100. In general, a shorter stub spar can be easier and cheaperto manufacture relative to a longer stub spar. Depending on a length ofthe stub spar 102, a quantity of material (e.g., torque material,centrifugal material, shear material or other material) of the stub spar102 can vary. For example, a shorter stub spar can have more materialthan a comparatively longer stub spar. Alternatively, the shorter stubspar can have substantially the same quantity of material as acomparatively longer stub spar, and can consequently be denser than thelonger stub spar.

The stub spar 102 is positioned at an inboard end 108 of the assembly100. In some implementations, the stub spar can have a substantiallyconstant thickness as the stub spar extends away from the inboard end ofthe blade assembly. the stub spar 102 tapers as the stub spar 102extends away from the inboard end 108 of the blade assembly. A ratio ofa quantity of material in the upper skin portion 102 and material in thelower skin portion 104 to a quantity of material in the stub spar 102 atthe inboard end 108 can be about 60:40 (or range between 55:45 and65:35). As the stub spar 102 tapers away from the inboard end 108towards the outboard end 110, the ratio of the quantity of material inthe upper skin portion 102 to the quantity of material in the stub spar102 and the ratio of the quantity of material in the lower skin portion104 to the quantity of material in the stub spar 102 increases. At theoutboard end of the stub spar 102, the ratio can be about 80:20 (or inthe range of 75:25 to 85:15). At the outboard end 110 of the assembly100, the ratio is 100:0 because the stub spar 102 does not extend a fullspan of the assembly 100. In some implementations, the outboard end ofthe stub spar 102 can include between one and three plies of material.Alternative implementations of the outboard end of the stub spar canhave different number of plies based on the design requirements of thestub spar.

In addition, at any cross-section along the stub spar 102, a percentageof torque material in the stub spar 102 can be greater than a percentageof torque material in either the upper skin portion 104 or the lowerskin portion 106. Similarly, at any cross-section along the stub spar102, a percentage of centrifugal material in the stub spar 102 can beless than a percentage of centrifugal material in either the upper skinportion 104 or the lower skin portion 106. For example, at anycross-section along the stub spar 102, substantially 10% (or a range of5% to 15%) of the centrifugal material is in the stub spar 102 and theremainder of the centrifugal material is distributed between the upperskin portion 104 and the lower skin portion 106. Similarly, at anycross-section along the stub spar 102, substantially 90% (or a range of85% to 95%) of the torque material is in the stub spar 102 and theremainder of the torque material is distributed between the upper skinportion 104 and the lower skin portion 106.

FIGS. 5A-5C show cross-sections of the rotor blade assembly 100 atdifferent lengths along the full span of the assembly 100. FIG. 5A showsa cross-section of the assembly 100 near the inboard end 108 of theassembly 100. At this location (502) of the assembly 100, the stub spar402 occupies a significantly larger portion than the upper skin portion404 and the lower skin portion 406. That is, a thickness of the stubspar 402 at the location 502 is substantially greater than a thicknessof the upper skin portion 404 or a thickness of the lower skin portion406.

FIG. 5B shows a cross-section of the assembly 100 away from the inboardend 108 of the assembly 100. At this location (504), the upper skinportion 404 and the lower skin portion 406 occupy a larger portion thanthe stub spar 402. That is, a thickness of the stub spar 402 at thelocation 504 is substantially less than the thickness of the upper skinportion 404 and the lower skin portion 406. In addition, a portionoccupied by the stub spar 402 at the location 504 is less than a portionoccupied by the stub spar 402 at the location 502 because the stub spar402 has tapered from the location 502 towards the location 504.

FIG. 5C shows a cross-section of the assembly 100 nearer to the outboardend 110 than to the inboard end 108. There is no stub spar at thislocation (506); instead, the entire portion of the assembly 100 isoccupied by the upper skin portion 404 and the lower skin portion 406.It follows then that, at an intermediate location between the inboardend 108 and the outboard end 110, a thickness of the stub spar 402 issubstantially equal to a thickness of the upper skin portion 404 or athickness of the lower skin portion 406.

At locations in which the stub spar 102 is thicker than the upper skinportion 104 or the lower skin portion 106, the stub spar 102 can includemore torque material (for example, torsional windings of compositefibers around a core) compared to the upper skin portion 104 or thelower skin portion 106. At locations in which the upper skin portion 104or the lower skin portion 106 is thicker than the stub spar 102, theupper skin portion 104 or the lower skin portion 106 can include morecentrifugal material (for example, composite fibers alignedsubstantially chord-wise on the span of the assembly 100). Alternativelyor in addition, the stub spar 102 can be made thicker than the upperskin portion 104 or the lower skin portion 106 at a location byincreasing a quantity of centrifugal material and torque material in thestub spar 102 at the location. Similarly, the upper skin portion 104 orthe lower skin portion 106 can be made thicker than the stub spar 102 ata location by increasing a quantity of centrifugal material and torquematerial in the upper skin portion 104 or the lower skin portion 106 atthe location.

FIGS. 6A-6C show cross-sections of examples of stub spars. FIG. 6A showsa cross-section of a stub spar 602 having a closed hollow cross-section.In the implementation shown in FIG. 6A, the stub spar 602 is made ofstructural composite material in the shape of an elongated, taperingtube that is hollow on the inside and whose ends are covered. Inaddition, the cross-section of the stub spar 602 is continuous and has,for example, a circular cross-section or a non-circular (for example,elliptical or other non-circular) cross-section without terminating inedges.

FIG. 6B shows a cross-section of a stub spar 604 having an open hollowcross-section. In the implementation shown in FIG. 6B, the stub spar 604is made of structural composite material in the shape of an elongated,tapering tube that is hollow on the inside and whose ends are open. Insome implementations, the cross-section of the stub spar 602 isdiscontinuous and has, for example, a horse shoe cross-section or othercross-section terminating in two edges.

FIG. 6C shows a cross-section of a stub spar 606 having a non-hollow (orsolid) cross-section. In the implementation shown in FIG. 6B, the stubspar 606 is made of structural composite material in the shape of anelongated, tapering tube that is filled with composite material on theinside so as to be non-hollow. In some implementations, a cross- sectionof the stub spar 606 can be similar to a cross-section of the stub spar602. Thus, the stub spar 602 and the stub spar 606 can be substantiallysimilar except that the former is hollow with closed ends while thelatter is solid.

In some implementations, the stub spar 102 can include only torquematerial and can exclude any centrifugal material. In suchimplementations, the stub spar 102 can include shear material. In someimplementations, the stub spar 102 can include only shear material andcan exclude any torque material or centrifugal material. In someimplementations, the stub spar 102 can include filler material.

In some implementations, the assembly 100 can include an abrasion stripassembly 112, a tuning weight 114 and a weight pocket 116 or any numberof details required for various uses of the blade. The stub spar can bemade of one of many types of constructions, for example, using onlyfabric plies, any number of lay ups, a multi-axis weave fabric or sock,or other constructions. The stub spar can include a scupper or a drainhole (or both) to prevent water from entering the blade. The abrasionstrip assembly 112 can taper off after a sufficient overlap with thestub spar to create an abrasion strip assembly 112 that is easy to form.The abrasion strip assembly 112 can have a grounding tab integral to theassembly 112 which can run a full length inboard of the taper to coverthe assembly 100.

FIG. 7 is a flowchart of a process 700 of manufacturing a rotor bladeassembly, for example, the rotor blade assembly 100. At 702, a stub sparis positioned between an upper skin portion and a lower skin portion.The stub spar extends less than a full span of the rotor blade assembly.Each of the upper skin portion and the lower skin portion extendsubstantially the full span of the rotor blade. The stub spar can taperas the stub spar extends away from an inboard end of the rotor bladeassembly. At 704, the upper skin portion and the lower skin portion areattached to the stub spar. In some implementations, a thickness of eachof the upper skin portion and the lower skin portion is configured tosupport substantially 30% (for example, between substantially 25% and45%) or more of the centrifugal loads by substantially 40% or less ofthe full span of the rotor blade assembly.

In some implementations, the upper skin portion and the lower skinportion can be attached to the stub spar by bonding or curing or both.For example, either the stub spar or the upper skin portion or the lowerskin portion (or any two or all of them) can be pre-cured beforepositioning the stub spar between the upper skin portion and the lowerskin portion. Alternatively, each of the stub spar, the upper skinportion and the lower skin portion (or any two or all of them) can beuncured. To attach the upper skin portion and the lower skin portion tothe stub spar, the upper skin portion, the lower skin portion and thestub spar can be bonded after attaching the upper skin portion and thelower skin portion to the stub spar. In some implementations, the upperskin portion and the lower skin portion can be attached to each otherand the stub spar can then be attached to, for example, inserted into acavity to snap fit with, the joined upper and lower skin portions.

II. Rotor Blade Assembly Including Thick Skins:

FIG. 8 is a schematic drawing of an example rotor blade assembly 800without a stub spar. The assembly includes an upper skin portion 804extending substantially a full span of the assembly 800. The assemblyincludes a lower skin portion 806 extending substantially the full spanof the rotor blade 800. An inboard end portion of the upper skin portion804 (i.e., a length of the upper skin portion 804 that is nearer theinboard end than the outboard end of the rotor blade assembly 800) isattached to an inboard end portion of the upper skin portion 806 (i.e.,a length of the lower skin portion 806 that is nearer the inboard endthan the outboard end of the rotor blade assembly 800). In someimplementations, the inboard end portion of the upper skin portion 804can be attached directly to the inboard end portion of the lower skinportion 806 without an intermediate member such as a spar.

In some implementations, each of the upper skin portion 804 and thelower skin portion 806 is configured to carry at least substantially 30%of the rotor blade assembly loads. As described above, the skins of aconventional rotor blade serve more as aerodynamic fairings thanstructural members. A percentage of the loads that such skins of theconventional rotor blade are configured to carry is very small, forexample, 5%-10% of the total blade loads. The skin portions of the rotorblade assembly 800, in contrast, are configured to carry comparativelygreater loads, for example, substantially 20%, 25%, 30%, 35% or more ofthe rotor blade assembly 800. For example, each of the upper skinportion 804 and the lower skin portion 806 is configured to carry atleast substantially 30% of the rotor blade assembly loads by less thansubstantially one-half of the full span of the rotor blade assembly 800.Substantially one-half of the full span of the rotor blade assembly 800can include, for example, exactly one-half or less than one-half, forexample, 47%, 45%, 40%, 35% of the full span.

Each of the upper skin portion 804 and the lower skin portion 806 can beconfigured to carry greater loads (relative to a conventional rotorblade) by increasing a quantity of material in the upper skin portion804 and the lower skin portion 806 compared to corresponding skins inthe conventional rotor blade assembly. For example, a quantity ofcentrifugal material or torque material (or both) in the upper skinportion 804 can be greater than a corresponding quantity in aconventional rotor blade. Similarly, a quantity of centrifugal materialor torque material (or both) in the lower skin portion 806 can begreater than a corresponding quantity in a conventional rotor blade.

In some implementations, each of the upper skin portion 804 and thelower skin portion 806 tapers from an inboard end 808 of the assembly800 towards an outboard end 810 of the assembly 800. A thickness of eachof the upper skin portion 804 and the lower skin portion 806 at theinboard end 808 can be greater than a thickness of each of the upperskin portion 804 and the lower skin portion 806 by a factor, forexample, of about four, six, eight, ten or greater. For example, theoutboard portion of the upper skin portion 804 or the lower skin portion806 (or both) can each have about 3-4 plies of material. The inboardportion of the upper skin portion 804 or the lower skin portion 806 (orboth) can each have about 30-40 plies of material.

In some implementations, the rotor blade assembly 800 can exclude a stubspar of any length. Alternative implementations of a rotor bladeassembly having an upper skin portion and a lower skin portion similarin structure and function to the upper skin portion 804 and the lowerskin portion 806, respectively, can include a stub spar that issubstantially similar in structure and function to the stub spar 102described above. In some implementations, the assembly 800 can includean abrasion strip assembly 812, a tuning weight 814 and a weight pocket816.

FIG. 9 is a flowchart of a process 900 of manufacturing a rotor bladeassembly. At 902, an upper skin portion is formed to extendsubstantially a full span of the rotor blade assembly. At 904, a lowerskin portion is formed to extend substantially the full span of therotor blade assembly. Each of the upper skin portion and the lower skinportion includes composite material to carry at least substantially 30%of rotor blade assembly loads. At 906, the upper skin portion isattached to the lower skin portion. In each of the upper skin portionand the lower skin portion, composite material to carry at leastsubstantially 30% of rotor blade assembly loads by less thansubstantially 50% of the full span of the rotor blade assembly loads canbe included. Each of the upper skin portion and the lower skin portioncan taper from an inboard end of the assembly toward the outboard end.In some implementations, a stub spar can be positioned between the upperskin portion and the lower skin portion similar to techniques describedabove.

III. Methods of Manufacturing Rotor Blade Assemblies

As described above, the spar of a conventional rotor blade is used tosupport and react dominant structural forces of the blade while the skincreates the aerodynamic surfaces. These designs consistently have issuescreating a repeatable bond between the skins and the rigid detailswithin. These defects, which are caused by issues associated with thisbond, are sometimes called skin voids and represent a significantportion of the defects in rotor blades. One technique to manufacture arotor blade assembly with thick skins can include stacking up compositematerial. Doing so can cause variations in the final surface contourproportional to a thickness of the laminate due to variations in bulkand location. To address this bulk factor concern, thick skins can betooled on the outer mold line (OML), thereby pushing the variance to theinner mold line (IML). The internal details of the blade can then bemade compliant to these surface variations resulting in high qualitybonds as well as aerodynamically pleasing surfaces. Resin transfermolding (or other net volume techniques) have also been used to createhigh quality aerodynamic surfaces with predictable mating surfaces.These techniques process place structure in a net volume mold and fillthe resulting space with resin. Inner mold line (IML) tooling can becheaper than net molding parts but can still produce a highly repeatableand reliable mating surface, for example, by reducing the number of skinvoids.

One technique to describe the rotor blade assemblies described here isto add an OML tooled stub spar and IML tooled upper and lower skiportions, which snap fit together. The stub spar can join the upper andlower skin portions. Since the adjoining surfaces are now the tooledsurfaces, variations in thicknesses are decreased. The stub spar createsa highly repeatable process for an IML tooled blade. The stub spar canbe optimized in the lug region such that it is (1) designed formanufacturing (DFM), and (2) structurally designed for the mechanicalperformance of both the lug and the spar. That is, the stub spar can bedesigned to provide the correct stiffness as well as handle loads (i.e.,stresses and strains) for each load case adequately.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made without departingfrom the spirit and scope of the disclosure. For example, the bladeassembly described here can be implemented to manufacture bladeassemblies for unmanned aerial vehicles (UAVs), sail plains and otherdevices that implement thin, highly loaded, high aspect ratio structureswhich attach at a single root joint. In some implementations, the stubspar can be a stub clip. As an alternative to incorporating some of thespar and shear material in the stub spar, an outer mold line (OML)tooled clip can be used to tie the two halves of the blade assemblytogether.

1. A rotorcraft rotor blade assembly comprising: an upper skin portionextending substantially a full span of the rotor blade assembly; and alower skin portion extending substantially the full span of the rotorblade assembly, wherein each of the upper skin portion and the lowerskin portion is configured to carry at least substantially 30% of rotorblade assembly loads.
 2. The rotor blade assembly of claim 1, whereineach of the upper skin portion and the lower skin portion is configuredto carry at least substantially 30% of rotor blade assembly loads byless than substantially 50% of the full span of the rotor bladeassembly.
 3. The rotor blade assembly of claim 1, wherein each of theupper skin portion and the lower skin portion tapers from an inboard endof the rotor blade assembly towards the outboard end.
 4. The rotor bladeassembly of claim 1, wherein a thickness of each of the upper skinportion and the lower skin portion at an inboard end of the rotor bladeassembly is about ten times a thickness of each of the upper skinportion and the lower skin portion at an outboard end of the rotor bladeassembly.
 5. The rotor blade assembly of claim 1, wherein, to carry atleast substantially 30% of rotor blade assembly loads, each of the upperskin portion and the lower skin portion comprises composite materialfibers oriented to carry torsional rotor blade assembly loads andcentrifugal rotor blade assembly loads.
 6. The rotor blade assembly ofclaim 1, wherein the rotor blade assembly excludes a spar.
 7. The rotorblade assembly of claim 1, further comprising a stub spar extending lessthan a full span of the rotor blade assembly.
 8. The rotor bladeassembly of claim 7, wherein the stub spar extends up to 50% of the fullspan of the rotor blade assembly.
 9. The rotor blade assembly of claim7, wherein the stub spar is positioned at an inboard end of the rotorblade assembly and wherein the stub spar tapers as the stub spar extendsaway from the inboard end of the rotor blade assembly.
 10. The rotorblade assembly of claim 9, wherein a ratio of a quantity of upper skinportion material and lower skin portion material to a quantity of stubspar material at the inboard end is about 60:40.
 11. The rotor bladeassembly of claim 10, wherein the ratio increases along the full span ofthe rotor blade assembly from the inboard end to the outboard end.
 12. Amethod of manufacturing a rotorcraft rotor blade assembly, the methodcomprising: forming an upper skin portion to extend substantially a fullspan of the rotor blade assembly; forming a lower skin portion to extendsubstantially the full span of the rotor blade assembly, wherein each ofthe upper skin portion and the lower skin portion includes compositematerial to carry at least substantially 30% of rotor blade assemblyloads; and attaching the upper skin portion to the lower skin portion.13. The method of claim 12, wherein forming the upper skin portion andforming the lower skin portion comprises including, in each of the upperskin portion and the lower skin portion, composite material to carry atleast substantially 30% of rotor blade assembly loads by less thansubstantially 50% of the full span of the rotor blade assembly.
 14. Themethod of claim 12, wherein each of the upper skin portion and the lowerskin portion is formed to taper from an inboard end of the rotor bladeassembly towards the outboard end.
 15. The method of claim 12, whereineach of the upper skin portion and the lower skin portion is formed suchthat a thickness of each of the upper skin portion and the lower skinportion at an inboard end of the rotor blade assembly is about ten timesa thickness of each of the upper skin portion and the lower skin portionat an outboard end of the rotor blade assembly.
 16. The method of claim12, further comprising: positioning a stub spar between the upper skinportion and the lower skin portion, the stub spar extending less than afull span of the rotor blade assembly; and attaching the upper skinportion and the lower skin portion to the stub spar.
 17. The method ofclaim 16, wherein the stub spar extends up to 50% of the full span ofthe rotor blade assembly.
 18. The method of claim 16, further comprisingforming the stub spar to taper as the stub spar extends away from theinboard end of the rotor blade assembly.
 19. The method of claim 18,wherein a ratio of a quantity of upper skin portion material and lowerskin portion material to a quantity of stub spar material at the inboardend is about 60:40.
 20. The method of claim 19, wherein the ratioincreases along the full span of the rotor blade assembly from theinboard end to the outboard end.